Branched-chain amino acids (BCAAs) are essential amino acids in tomato (Solanum lycopersicum) required for protein synthesis, which also modulate growth and abiotic stress responses. To date, little is known about their uptake and transport in tomato especially under abiotic stress. Here, the tomato amino acid permease 6 (SlAAP6) gene was identified as an amino acid transporter that restored mutant yeast cell growth on media with a variety of amino acids, including BCAAs. Overexpression of SlAAP6 (SlAAP6-OE) in tomato raised the BCAA content and elevated the fresh weight, while SlAAP6 knockouts (slaap6) showed reduced levels of neutral and basic amino acids in seedling tissues and lower total free amino acid distribution to shoots. In comparison to wild type (WT) and slaap6 mutants, SlAAP6-OE alleviated root limited growth by elevated BCAA transport and upregulated the expression of root-growth-related genes by increasing BCAAs in vivo. As SlAAP6 serves as a positive regulator for BCAA abundance, SlAAP6-OE lines showed greater salinity tolerance, while slaap6 mutants exhibited increased salt sensitivity. The salt tolerance of SlAAP6-OE plants was further enhanced by the application of exogenous BCAAs. In addition, BCAA supplementation reduced the accumulation of H2O2 in root under salt stress conditions. Based on these findings, SlAAP6-mediated uptake and transport of BCAAs facilitated growth and salt tolerance in tomato. By characterizing this key amino acid transporter, this study provides a novel approach to simultaneously enhance tomato nutritional quality, growth and development, and stress resistance through genetic improvement.

中文翻译：

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氨基酸通透酶 SlAAP6 通过介导支链氨基酸转运促进番茄生长和耐盐


支链氨基酸 （BCAA） 是番茄 （Solanum lycopersicum） 中蛋白质合成所需的必需氨基酸，还调节生长和非生物胁迫反应。迄今为止，人们对它们在番茄中的吸收和运输知之甚少，尤其是在非生物胁迫下。在这里，番茄氨基酸通透酶 6 （SlAAP6） 基因被鉴定为氨基酸转运蛋白，可恢复突变酵母细胞在含有多种氨基酸（包括 BCAA）的培养基上的生长。番茄中过表达 SlAAP6 （SlAAP6-OE） 提高了 BCAA 含量并提高了鲜重，而 SlAAP6 敲除 （slaap6） 显示幼苗组织中中性和碱性氨基酸水平降低，总游离氨基酸分布在芽中。与野生型 （WT） 和 slaap6 突变体相比，SlAAP6-OE 通过增加 BCAA 转运减轻根限制生长，并通过增加体内 BCAA 上调根生长相关基因的表达。由于 SlAAP6 是 BCAA 丰度的正调节因子，因此 SlAAP6-OE 细胞系表现出更高的耐盐性，而 slaap6 突变体表现出更高的盐敏感性。外源 BCAA 的应用进一步增强了 SlAAP6-OE 植物的耐盐性。此外，在盐胁迫条件下，BCAA 添加减少了根系中 H2O2 的积累。基于这些发现，SlAAP6 介导的 BCAA 摄取和转运促进了番茄的生长和耐盐性。通过表征这一关键的氨基酸转运蛋白，本研究提供了一种通过遗传改良同时提高番茄营养品质、生长发育和抗逆性的新方法。